The objective of this work was to apply the simplified equation of viability developed by Andreoli (1998), to predict changes in seeds viability during open warehouse storage. Seeds of wheat cultivars BRS 210, BRS 208, CD 104, IAPAR 78 and IPR 85 were packed in raffia bags and stored for 0, 30, 60, 90, 120, 180, 240, and 300 days in an open warehouse at two locations: Mauá da Serra and Londrina; both in Paraná State, Brazil. The simplified equation is given by the model Vp = Vi - (tgb).p, in which Vp is seed viability in probit for a period p (days), Vi is the initial seed viability in probit and tgb is the seed deterioration rate for wheat at determined storage conditions. The germination data was transformed in probit and the deterioration rate (tgb) between 0 and 30 days was calculated.The coefficient tgb ranged from 0,4 x10-3 to 1,3 x10-3, depending on locations and cultivars. In Londrina, the coefficient tgb was higher, indicating that the germination declined faster than Mauá da Serra. This model has accurately predicted wheat seeds germination, independently of the genotype, under open storage. The initial quality of the seed (V1) did not affect the seed deterioration rate.